Electrical cable

ABSTRACT

A multi-core electrical cable for use in the supply of electricity to certain electrical devices such as vapor lamps and the like comprises a molded-on outer sheath and at least two separately insulated inner core cables. At least one of the core cables has a high tension conducting core with an overall cross-sectional area of at least 1 mm square. Preferably, the high tension conducting core comprises a bundle of at least 32 strands of 0.2 mm diameter tinned copper wire with an insulating sheath which is at least 1.8 mm thick. The molded-on outer sheath of the multi-core cable preferably totally encapsulates the inner cables to a depth of at least 1.3 mm.

TECHNICAL FIELD

The present invention relates to an electrical cable or flex and inparticular to a high voltage electrical cable.

BACKGROUND ART

In the supply of electricity to certain electrical devices it is oftennecessary for the cable or flex used to withstand an initial highelectrical voltage which is used to commence operation of the device,which thereafter runs on a standard mains voltage. For example, in orderto strike a mercury vapour lamp or other similar lighting means, it isnecessary to supply an initial voltage of approximately 4,500 volts. Ifa standard 3-core 13 amp electrical cable is used to supply thisvoltage, the cable can cope initially but quickly becomes burnt out withrepeated use. There is also a significantly increased risk of fire.

To overcome the problem of supplying an initial high voltage to devices,such as lamps, which then run on a standard mains voltage, a heavy gaugesingle core insulated cable is often used as the live wire of theelectrical supply along with separate standard single core neutral andearth wires. When wiring such a device to a mains electric supply thesethree wires are often pulled into a hollow sheath or tubular casing bythe electrician so that the resulting single flex can be threaded, asappropriate, down a conduit between the electrical supply and thelocation of the device. However, it will be appreciated that thisconsiderably increases the work required by the electrician as comparedwith the wiring of a device capable of being supplied by a standard3-core cable. In addition, the sheathing of the three separate wires inthe outer casing is often difficult to accomplish satisfactorily as thecasing tends to twist and wrinkle.

The object of the present invention is to overcome or substantiallymitigate the aforementioned problems.

SUMMARY OF THE INVENTION

According to the present invention there is provided a multi-coreelectrical cable comprising a moulded-on outer sheath, at least twoseparately insulated inner core cables and a separately insulated earthcable and characterised in that at least one of the inner core cableshas a high tension conducting core with an overall cross-sectional areaof at least 1 mm² and an insulating sheath which is approximately 1.8 mmthick, and in that the earth cable has a conducting core with an overallcross-sectional area of at least 1 mm² and an insulating sheath which isapproximately 0.65 mm thick.

Preferably, the high tension conducting core comprises a bundle of atleast 32 strands of 0.2 mm diameter tinned copper wire.

Preferably also, the moulded-on outer sheath of the multi-core cabletotally encapsulates the inner core cables and the earth cable to adepth of at least 1.3 mm.

Preferably also, the inner core cables and the earth cable are twistedtogether within the moulded-on outer sheath and bound by a spirallywound tape.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example withreference to the accompanying drawing, in which:

FIGS. 1 and 1a are side and end views respectively of a high tensioncore cable for incorporation into a multi-core cable according to theinvention;

FIGS. 2 and 2a are side and end views respectively of an earth safetycore cable for incorporation into a multi-core cable according to theinvention;

FIGS. 3 and 4 are side views of three core cables forming part of amulti-core cable according to the invention at two stages respectivelyduring its manufacture;

FIG. 5 is a side view of a multi-core cable according to the inventionwith part of its outer sheath cut away to reveal the core cables; and

FIG. 6 is a transverse cross-sectional view of the cable shown in FIG.5.

DETAILED DESCRIPTION OF THE INVENTION

The multi-core cable of the present invention comprises at least oneinner core cable 1, as shown in FIG. 1 and 1a, which is capable ofwithstanding a high voltage, preferably of at least 4,500 volts.

This cable 1 comprises an insulating sheath 2 encapsulating an innerconducting core 3 which is made up of a bundle of individual wires 4.Preferably, each wire 4 is a tinned copper wire of approximately 0.2 mmdiameter so that the overall cross-sectional area of the conducting core3 is approximately 1 mm².

The insulating sheath 2 encapsulates the core 3 to a depth "a" of atleast 1.8 mm as shown in FIG. 1a and is preferably made from a PVCcompound which complies with British Standard BS6746. However, any othersuitable insulating material could be used, such as for example siliconeor rubber, provided that it can withstand a high electrical voltage. Inthis case, the depth of the encapsulation of the core 3 by the sheath 2may be different according to the material used.

FIGS. 2 and 2a show a safety earth cable 5 for incorporation in amulti-core cable according to the invention and comprising a hightension core cable as shown in FIGS. 1 and 1a. The cable 5 againcomprises an insulating sheath 6 encapsulating an inner conducting core7. As with the high tension cable 1, the core 7 of the cable 5 is madefrom a bundle of individual wires 8 and again these comprise 32 tinnedcopper conducting wires of 0.2 mm diameter. However, the depth of theinsulating sheath 6 encapsulating the core 7 need not be so great asthat for the cable 1 as the earth cable 5 is intended to withstand ahigh voltage only in exceptional circumstances. Here, the sheath 6 has adepth "b" of 0.65 mm surrounding the core 7 and it is made from the samePVC material as the sheath 2.

A multi-core cable according to the invention suitable for use insupplying an electrical current to a mercury vapour lamp or similarwhere it will have to withstand an initial voltage of the order of 4,500volts preferably comprises three cores, as in a standard electricalcable or flex, but with the live and neutral core cables being hightension cores of the kind described above with reference to FIGS. 1 and1a and the safety earth core cable being of the kind described withreference to FIGS. 2 and 2a. The construction of such a cable will nowbe described with reference to FIGS. 3 to 6.

In the manufacture of such a three-core cable, the high tension live andneutral cables 9 and 10 respectively and an earth cable 11 areindividually manufactured in known manner to the specificationspreviously described and they are then lightly twisted together as shownin FIG. 3. Preferably, to aid the identification of each of the cables9, 10 and 11 for wiring purposes, the insulating sheath of each isindividually coloured in line with International Standards.

After twisting, the bundle of cables 9, 10, 11 is secured by theapplication of tape 12, which is wound spirally around the bundle oftwisted cables 9, 10, 11. The tape 12 is clear so that the colours ofthe sheaths of the cables 9, 10 and 11 can be seen if the finishedmulti-core cable 13, as shown in FIGS. 5 and 6, is cut into.Additionally, the tape 12 is also made from an electrically insulatingand heat resisting material.

Finally, the taped and twisted cables 9, 10 and 11 are completelyenclosed in known manner in a moulded-on sheath 14 which can be made ofa similar PVC compound as that of the individual sheaths comprising thecables 9, 10, 11. The sheath 14 encapsulates the twisted bundle ofcables 9, 10, 11 to a depth "c" of at least 1.3 mm and also insulateseach of the cables from one another so that the finished structure ofthe cable 13, as shown in FIG. 6, is solid. The overall diameter "d" ofthe cable 13 is of the order of 12.5 mm.

Such a multi-core cable 13 is suitable for use in many situations andparticularly in lighting installations where a high voltage of up to4,500 volts has to applied to an electrical device. However, it will beappreciated that many different configurations of cable are possibledepending on their intended use. Cables with 1, 2, 3, 5 and more innerhigh tension inner core cables are all possible and can be manufacturedin a similar way to that described above for use in a variety ofapplications where high voltages must be withstood.

We claim:
 1. A multi-core electrical cable comprising a moulded-on outersheath, at least two separately insulated inner core cables and aseparately insulated earth cable, at least one of the inner core cableshas a high tension conducting core with an overall cross-sectional areaof at least 1 mm² and an insulating sheath which is approximately 1.8 mmthick, and wherein said earth cable has a conducting core with anoverall cross-sectional area of at least 1 mm² and an insulating sheathwhich is approximately 0.65 mm thick.
 2. The cable as claimed in claim1, said high tension conducting core comprises a bundle having at least32 strands of 0.2 mm diameter tinned copper wire.
 3. The cable asclaimed in claim 1, said moulded-on outer sheath of the multi-core cabletotally encapsulates the inner core cables and said earth cable to adepth of at least 1.3 mm.
 4. The cable as claimed in claim 1, said innercore cables and said earth cable are twisted together within saidmoulded-on outer sheath and bound by a spirally wound tape.
 5. The cableas claimed in claim 1 comprising at least two separately insulatedhigh-tension conducting cores.